Method and apparatus for continuous exploration of bore holes



March 14, 1939. J. J. JAKOSKY 2,150,159

METHOD AND APPARATUS FOR QONTINUOUS EXPLORATION OF BORE HOLES Filed March 9, 1937 III//////// R, s O Y 0 H mm m y h,

Patented Mar. 14, 1939 UNITED STATES, PATENT OFFICE METHOD AND APPARATUS FOR CONTINU- oUs ExrLoaA'noN or onn HOLES John Jay Jakosky, Los Angeles, Calif.

Application March 9, 1937, Serial No.129,839

1': Claims. (01. 115-132) This invention relates to a new method and into a bore hole and is exposed to electrical conapparatus constituting an improvement in the tact with the wall of the bore hole substantially art of determining the character and nature of throughout its length, may be satisfactorily emthe strata traversed by a bore hole, and more ployed as an electrode in an electrical system-for 5 particularly it relates to the determination of the determining the nature and characteristics of the 5 characteristics of the strata traversed by a bore strata adjacent the lower end of said drilling hole while the drilling operations are in progress. apparatus, without the necessity of insulating one This application is a continuation-in-part of my portion of the drilling apparatus from another or pending application Serial No. 94,063, filed August from the earth adjacent the mouth of the bore 3, 1936. hole. V

The principal object of the invention is to pro- An essential feature of the present invention,

. vide a method and apparatus which will give a which makes it possible to employ anon-insulated visible, instantaneous, and preferably permanent and exposed electrically conductive drilling aprecord at the surface, as the drilling operations paratus in a bore hole as one electrode, consists l5 progress. Such records are of great value during in connecting the other electrode to the earth at drilling operations, especially in areas where-the a positionsufficiently removed from the bore hole drilling must be stopped at a known horizonor so that the electrical measurements taken bestrata, as for instance when drilling intoa high tween said electrodes areinfluenced to an impressure oil sand, or when drilling through an por a t degree y Variations in an electrical oil sand, and where water may be encountered by property, such as'natural earth potential, resist- 20 a stratum underlying the oil sand. By means of ance impedance, or dielectricproperties, of the the present method and apparatus suitable indi strata adjacent the lower end of the drilling apcatlng and signaling means. may be located on paratus. When the last-named ordistant electhe surface of the ground and the drilling operatrode is removed'from the bore hole a distance tions supervised more intelligently. greater than one-third the depth which the 2 5 A prior method has been suggested for this drilling apparatus extends within the bore hole,

work, embodying an insulated drillpipe, or an the I condition for' satisfactory measurements insulated conductor extending down inside of a which reflectthe electrical properties of the strata drill pipe, and a bit which is insulated from the adjacent the lower end of the drilling apparatus drill pipe. The current flows from this insulated is usually satisfied. I

bit into the strata. The other terminal of the Thus, when passing an electric current through current circuit is at the surface of the ground the earth between the drilling apparatus, which near the mouth of the hole, or it may be the includes the surface equipment, the drill stem drill pipe itself. Suitable measuring instruments and the drillbit, in the case of a rotary drilling are included in this circuit for measuring variaapparatus, and another electrode connected to 3.)

tions in current and/or potential as the bit the earth at a position sufficiently removed from descends the hole. Afterrepeated and extensive the bore hole, the path of the current will in gentests at commercial operations, the method has. eral be through the earth between all parts of the proven to be of limited us'e due to, the difiiculty drilling apparatus and the last-named electrode.

40 of properly insulating the. drill pipe from the By removing this last-named electrode a suflicient 40 bore hole itself, ory-of passing an insulated wire distance from the bore hole the electrical chardown the inside of the drill pipe. Another pracacteristi'cs of this current path through the tical difliculty in the latter method is to obtain ,earth, and consequently the measurements obproper insulation of the bit from the drill pipe. tained as the drill is extended to different depths Insulating materials of this type are not usually in the hole, are influenced to an important de- 45 of sufiicient mechanical rigidity and ruggedness I gree by the electrical properties of the strata adto withstand the severe conditions encountered jacent the. lower end of the drilling apparatus.

in drill work. In the method which is described This feature of my invention may be attributed in this invention, these practical difliculties have to the flow of the current along and parallel to been overcome, and in addition a simplified the beddingplanes of the strata adjacent the 50 method of operation provided. which combines lower end of the drilling apparatus, as described greater accuracy. in my pending application Serial No. 55,600, filed A particular object of this invention is to pro- December 21, 1935. vide a'method and apparatus in which a conven- An important feature of this invention, theretional form of drilling apparatus, which extends fore, is the employment. of the distant electrode.

to give a readable or detectable change on the total current flowing in the circuit, as difierent strata-are penetrated by the bit.

While the foregoingf practical advantages of this improvement are of major importance, the method and apparatus contain certain important features of construction and arrangement which will become manifest as the process is studied, by reference to the following specifications and drawing, wherein:

Fig. 1 illustrates the essential parts of the conventional equipment employed in the rotary drilling of bore holes;

Fig. 2 is a diagrammatic illustration of one form of electrical circuit which may advantageously be employed in conjunction with various types of drilling apparatus;

Fig. 3 shows a portion of the recorded data or graph obtained in the usual rotary drilling operations, when my invention is applied;

Fig. 4 illustrates an arrangement which may be employed for directly recordingdzhe relationship between depth and electrical characteristics; and

Fig. 5'is a diagrammatic representation of an alternative circuit arrangement which may be used in conjunction with the circuit shown in Fig. 2.

trade connected to the earth at Fig. 1 illustrates the application of this invention to the conventional rotary system of drilling. In this figure, the rotary table I is connected to a proper source of motive power la.

The rotary table. by means of the Kelly joint 2 transmits a rotary motion to the drill stem 3 extending within the bore hole H. At the end of the drill stem is the drilling bit 4. The Kelly joint is supported at its upper end by the swivel head In. These parts constitute the usual type of rotary drilling equipment and need not be described in detail herein. A connection terminal II is in electrical contact with the swivel-head and associated drilling mechanism including the drill stem 3'and bit 4 and is associated with a suitable electrical energizing and measuring circuit, such as hereinafter described, for establishing an electrical circuit through the earth between the drilling apparatus and another eleca position remote from the bore hole. V

The present invention is also applicable to various types of rotary drilling equipment and drilling bits, including various devices for obtaining rock samples, and to core-bits. In addition, the invention may be applied to cable drilling apparatus wherein a heavy bit assembly impacts and cuts into the earth by being alternately raised and lowered on a steel cable. The invention may also be applied to hydraulic drilling methods employing'a pipe, extending into the bore hole, from which water under high pressure is being discharged. In short, the method and apparatus of this invention may advantageously be employed with any exploring and/or drilling apparatus which is constructed of, or employs, electrically conductive material or fluids.

One type of electrical circuit which may be employed for measuring the changes in resistance or impedance, as the drill penetrates the earth, is illustrated in Fig. 2. It will be understood, however, that any of the conventional circuits may 5 be a function of the impedance of such formations. Broadly, it may be said that the measurements serve to indicate variations in the conductivity of the formations, the term conductivity being considered herein as including either straight conductance (the reciprocal of resist- 2 ance) in the case of direct current, or admittance (the reciprocal of impedance) inthe case of alternating current.

Electrical connection to the rotary drill stem may be made by means of terminal II, as above 2 described and the other contact to the earth is made by means of a suitable surface electrode 5, preferably of large contact area, placed a considerable distance from the hole. This distance is preferably one-third (or more) of the depth sential that this resistance be of a fixed nature,

inasmuch as any variation in it will cause variations in the recorded data. I have found that the electrode should preferably be placed a distance of two to five feet below the surface of the ground, in order to prevent changes in. conductivity due to changes in temperature between night and day, and changes caused'by drying out of the soil or its wetting after a rain. The casing of a distant well may be utilized as a distant electrode, or a suitable electrode may be lowered 4 into contact with the conductive fluid in a distant well for this purpose.

One arm, such as b--d, of the conventional Wheatstone bridge indicated generally at W is a variable resistor 6 which may be adjusted to equal the resistance of the well-distant electrode circuit at the start of the drilling and'measuring operations. The points a and d of said bridge are shown as connected by conductors l5 and I6, respectively, to the drilling apparatus and 5 the distant electrode 5. The power supply means I3 for the Wheatstone bridge may be any source of constant potential supply, either direct current or low frequency or high frequency alternating current. In a majority of cases it is convenient 6 to employ or cycle alternating current available at the rig. In the latter case, it is preferable to employ a small, well insulated transformer, in order to isolate the measuring circuit from the power supply which is oftentimes grounded. The power supply is impressed across the bridge circuit at points c-d. An ammeter 1 is connected in series with the power supply means for showing the total current flowing in the bridge circuit,'and a second ammeter 7 8 connected in conductor I5 shows the current flowing in the well-distant electrode circuit. Connected across the arms of the bridge,between points a-b, isa vacuum thermocouple 9, which across the bridge, as the conductivity of the earth's circuit is changed. The output of the vacuum thermocouple is connected to a suitable continuously recording meter I2, which. usually records variations in the bridge potential versus time. ,In' case the potential supplied by source I3 is subject to material fluctuation, I prefer to employ a compensating thermocouple 9' whose input is connected in shunt with a variable resistance H in the line leading to the bridge and whose output is connected in series with the output of thermocouple 9, but in reverse relation thereto. 1 k

It will be seen that any typeof measuring arrangement may be employed. but the vacuum thermocouple as described constitutes a particularly stable system for measuring these changes during the drilling operation. The vacuum thermocouple has a sufficient time lag so as to minimize the effect of transitory variations or fluctuations in the electrical circuit, such as minor and unimportant variations caused by changes in electrical conductivity as the drill stem and drill momentarily come in contact with different portions of the drill-hole wall and casing, as the drill and drill stem rotate. Due to the low power output of the vacuum thermo couple, it is preferable to employ it in conjunction with some type of sensitive photographic re cording system.

It will be seen that when an electric current is passed through the .earth between the drilling apparatus and the distant electrode 5, as by means of an associated power supply circuit such as above described, the current will flow between the earth and the drilling apparatus throughout substantially the entire length thereof, particularly when the bore hole contains a conductive fluid medium such as the aqueous drilling fluid ordinarilyemployed in rotary drilling operations. However, if the distant electrode is sufficiently removed from the bore hole a measurable portion of the current will flow throughout substantially the entire length of the drill stem-or other drilling apparatus extending within the bore hole, and through the strata adjacent the lower end of the'drilling apparatus. It is this current flow, which is measurable if the distant electrode is removed a sufficient distance from the bore hole, which gives electrical variations indicative of the nature of the strata adjacent the lower end of the drilling apparatus, as the drilling apparatus is moved to differentdepths.

Application of this invention to conventional drilling operations may be summarized briefly as follows:

Measurements may be made at any time after drilling operations have started. The measurements should begin, however, at a time when the strata exhibit characteristic electrical changes which may be employed for correlation purposes. In some areas; important electrical markers (strata which may readily be recognized by characteristic changes in electrical properties) manifest themselves many hundreds of feet above the oil sands, while in other areas important markers are encountered adjacent to the oil sands. In

metal mining operations, the measurements should begin prior to the time the drill penetrates the mineral-bearing formations. For location of water-bearing horizons the measurements also should begin prior to the time the bit penetrates the water-bearing formation.

The electrical apparatus, diagrammatically illustrated in Fig. 2, is connected to the drilling mechanism and the distant electrode by means of suitable insulated wires. The bridge resistor 6 is adjusted to give a suitable position of the recording pen or light beam (preferably to the inner margin of the paper, when an increase in conductivity results in movement of the recording line to the right) on the sheet [2. If variations in power supply are noticeable, the resistor l4 should be adjusted to minimize these variations.

It will be recognized that when the drill is penetrating a medium of homogeneous conductivity, the recording line will gradually shift or drift to the right, inasmuch as more contact area is being exposed to the medium, resulting in an increase in conductivity and resultant current flow. When the drill penetrates a stratum of different electrical conductivity there will be a change in the slope of the recordingline. If, for instance, the drill passes out of a good conducting medium into a highly resistant medium, there will be a change in the slope of the line, since there will be less drift for a given time interval. Interpretation of the data will necessitate, however, that consideration be given the different rates of penetration of the drill in strata of different degrees of hardness. the drill will penetrate feet of a soft shale formation in less time than it will penetrate 10 feet of a harder formation. As a result the slope of the line is dependent as much upon the rate of drill penetration as upon the electrical properties of the strata. Before interpretation may be For instance,

made of the record, under the extreme conditions just mentioned, the depth of penetration'of the drill at given time intervals must be obtained from the drillers records. Final interpretation is therefore based upon changes in slope versus depth of penetration.

arrangement has the advantage of giving more power, which may be employed for actuating a heavier type of recording mechanism. If the triode tube is used, a pen-actuated stylus may be employed, giving a direct, visible reading of the variations in current 'on a paper chart.

Various types of continuous recording meters or systemsmay be employed, but one which has proven practical in operation is of a type which records the changes in current or potential versus time. The meter mechanism is actuated by means of a power amplifier vacuum tube, con nected as described in the above paragraph. A record of this type gives considerable informa tion tothe drilling superintendent, besides merely the electrical properties of the strata passed through. For instance, all information relative to actual time of drilling, time consumed in going in and out of the hole, and time idle, is shown clearly on the chart. 'As the drilling proceeds, the resistance or impedance of the earth circuit naturally decreases, due to the larger contact area and the increased cross-sectional area of the path of current now through the earth as the hole deepens. This results in a small but continual drift of the chart as shown in Fig. 3.,

' as further drilling progresses, it resumes its in the electrical characteristics of the strata penetrated by. the drill bit, and difierences in the slope of different portions of the curve will indi cate diiferences in conductance or other electrical characteristics of the strata at two corresponding depths.

. When the drilling operation stops, as marked at point a, the record is a practically straight line, from jto It. When the tools start out of the hole as at point It, there is a decrease in conductivity due to the decrease in. effective electrode area, and the current decreases as shown between it and Z. During the period that the tools are out of the hole, as between I and m, a straight line occurs. As the drill isbeing lowered to the bottom of the hole, the curve shifts to the right rapidly, as between m and n, and

gradual shift to the'right, as from n to 0. V

It will readily be seen that instead of using the continuous roll-type paper recording system, it is possible to employ the conventional circular recording chart. If desired, the chart may be allowed to make more than one revolution because the drift will cause the average recording line to spiral inward or outward, depending upon whether the chart mechanism is moving inward or outward for a decrease in resistance, impedance or the other electrical properties being measured. Due to this spiraling effect the condition obtained when a homogeneous medium is drillers log the depth which the drill has reached for any certain period of time. In. this manner the changes in electrical properties of the strata' at different depths can be ascertained.

This invention also contemplates a recording method showing the relationship between electrical properties and actual depth. This may comprise a. depth-recording system utilizing a measuring wheel frictionally held against the drill pipe as it descends the hole. This measuring wheel may actuate a gear system which in turn drives the recording paper.

Another method for showing the relationship between electrical properties and actual depth is diagrammatically illustrated in Fig; 4. In this figure the drilling assembly comprising a Kelly joint 2, supported by the swivel head l0, and the drill pipe and bit in the hole, is supported by a sheave wheel l8. Steel cables l9 are threaded through the sheave wheel' over the .crown block 20 at the top, of the derrick 2|. A small steel flexible cable 22 is connected to the sheave wheel I8. This cable passes over idler pulleys 23 and 23a, to the r'ecording mechanism which is located at a convenient place on the derrick floor. The recording mechanism is actuated by movement of the cable 22 as the sheave block l8 moves upward and downward during the drill-- ing operations. The actuating mechanism comprises a drum 24 on which the flexible cable 22 is wound. A sufiioient number of turns are placed -on the drum in order to allow the sheave block drilling operations are in progress, that is, when nected't'o the driving assembly 30 and 3|.

' a suitable transformer l1.

the ratchet wheel. 30. This ratchet wheel drives a sprocket wheel 3I' which meshes with perforations along the edge of the recording paper 28. As the bit descends the hole the paper 28 is moved forward and a record made by means of the pen recorder, shown diagrammatically at 32. An idler wheel 29 is employed for rigidly supporting the paper as it passes the recording pen. The unused paper is on spool 28 and the used paper is on spool 21. Both of these spools are driven by means of proper spring belts con- The idler 29 is preferably placed from 12 to lflinches from the drive sprocket 3| in order that visual observations may be made of the record as thedrilling progresses.

When thepawl 25a, engages the ratchet wheel 30, it will be seen that the paper is moved forward as the bit descends the hole. After the desired increment of drilling operation has been completed and it is desired to come out of the hole, the pawl 25a is manually disengaged from the ratchet wheel 30. The Kelly joint is now disengaged from. the drill stem, and another section of drill steminserted in the assembly. The bit is now lowered to the bottom of the hole and the pawl "2511 again engaged. As the drilling operations are resumed, the record is continued. When'it is desired to come out of the hole, the pawl 25a is disengaged. In some instances it is desirable to reverse movement of the paper, and this may be accomplished by engaging pawl 25. By means of an interlocking control between the pen recorder 32 and the pawl contacts, no record is usually made on the paper when its direction of movement is reversed. v

An alternative circuit arrangement is shown in Fig. 5 in which the power supply and measuring circuit or circuits may be isolated from or indirectly associated with, the electrode circuit. Referringto said figure, I have shown the conductors l5 and I6 which emanate from the bridge W of Fig; 2, connected to one winding of The other winding of said transformer is shown connected through conductors l5 and I6 to the terminal II on the swivel head l0 and the distant electrode 5, respectively. Such a circuit arrangement may be advantageously employed as an alternative to the arrangement shown in Fig. 2 whenalternating current measurements are being made.

' It will be appreciated that numerous forms of measuring circuits and procedures may be employed in carrying out the method of this invention. For example, earth potential measurements may be taken with a suitable indicating or recording instrument associated with the two electrodes for measuring changes in potential, while measurements which depend upon the passage of current through the strata may be taken with a. large variety of circuits. For example, the source of current may be directly associated with the electrodes as shown in Figs. 1 and 2,.when either direct or alternating current is used, or it may be indirectly associated with the electrodes, as through a transformer as shown in Fig. '5, when alternating current is used. Furthermore, the electrical measuring means may be directly associated with the electrical circuit associating the two electrodes, as when a direct or alternating current ammeter is connected in the electrode circuit, or it may be indirectly associated as through transformers or other means in the case of some alternating current measurements.

Also the method may be practiced by maintaining a constant potential at the source-of current and making a record of the variations in current as the drilling apparatus is moved to different depths, or the current may be maintained constant and the value of potential required to maintain the constantcurrent may be recorded, or a record may be made of both current and potential.

Electric current is used to embrace both direct and alternating currents. Direct currents may be defined as either continuous, or pulsating currents in some instances, while alternating currents may include commercial alternating currents, medium and high frequency currents, and, in suitable instances, recurring pulsatory currents.

Natural earth potential measurements may also be obtained by connecting the drilling systemand the distant electrode to the input circuit (gridfilament) of the triode tube, or to the input circuit of a vacuum thermocouple, the output circuit 1 being in either case connected to a suitable electrical measuring means in a manner comparable 'to that above described. Changes, and often reversals, in the natural earth potentials are obtained as the drill penetrates different strata. These changes in potential are probably due to (l) the non-uniform distribution of lateral flowing current with depth, and (2) differences in chemical properties of the natural earth waters in the various strata.

It will be understood that, instead of taking continuous electrical measurements as above described, a series of separate electrical measurements may be taken at suitable frequent intervals of time or depth, the purpose being, in general, to obtain measurements of the electrical characteristics of the portion of the earth included electrically between the drill pipe and the remote electrode, with the drill pipe extending to different depths within the bore hole.

Such electrical characteristics may include naturally occurring earth potentials, or electrical properties obtainable through the passage of current through the earth. These last-named properties or characteristics may include resistance, conductivity, impedance, reactance, dielectric properties, phase-shift, etc., dependent upon the circuits used to pass the current through the earth and the circuit and type of electrical measuring means used to recognize such properties. In any event the electrical properties of the strata are determined by variations produced on a suitable electrical measuring means, in response to variations in an electrical variable, produced by variations in said electrical properties of the dif-, ferent strata as the drilling apparatus traverses the bore hole.

I claim:

1. A method'for determining variations in an electrical property of the strata at different depths traversed by a bore hole during the process of drilling said bore hole, which comprises: taking a measurement of an electrical variable in an electrical circuit comprising a drilling apparatus extending within a bore hole and serving as an electrode, another electrode connected to the earth at a position removed from said bore hole, and the portion of the earth included electrically between said electrodes; and repeating such measurement as said drilling apparatus is extended to different depths, while maintaining said other 16 electrode substantially at a fixed position, said drilling apparatus being exposed to electrical contact with the wall of said bore hole throughout substantially its entire-length, and said other electrode being sufiiciently distant from the bore hole so that the measurements obtained are infiuenced to an important degree by variations in an electrical property of the formation adjacent the lower end of the drilling apparatus.

2. A method for determining variations in an electrical property of the strata at different depths traversedby a bore hole during the drilling of said bore hole, which comprises: passing an electric current through the earth between an electrode comprising a drilling apparatus extending within a bore hole, and another electrode connected to the earth at a position removed from said bore hole; taking a measurement of an electrical variable indicative of the electrical conductivity of the path of said current through the earth; and repeatingthe passage of such current and the taking of such measurement as the drilling apparatus is extended to different depths within the bore hole, while maintaining said other electrode substantially at a fixed position, said drilling apparatus being exposed to electrical contact with the Wall of said bore hole throughout substantially its entire length-whereby the flow of said electric current between the drilling apparatus and the earth is caused to take place throughout substantially the entire length of said drilling apparatus, and said last-named electrode being sufficiently removed from said bore hole so that variations in electrical conductivity of the strata adjacent the lower end of the drilling apparatus produce measurable variations in the measured electrical variable as said drilling apparatus is extended to diiierent depths.

3. A methodior determining variations in an electrical property of the strata at different depths traversed by a bore hole during the drilling of said borehole, which comprises: passing an alternating electric current through the earth between an electrode comprising a drilling apparatus extending within a bore hole, and another electrode connected to the earth at a position removed from said bore hole; taking a measurement of an electrical variable indicative of the electrical impedance of the path of said current through the earth; and repeating the passage of such current and the taking of such measurement as the drilling apparatus is extended to different depths within the bore hole, while maintaining said other electrode substantially at a fixed position, said drilling apparatus being exposed to electrical contact with the wall of said bore hole throughout substantially its entire length whereby the flow of said electric current between the drilling apparatus and the earth is caused to take place throughout substantially the entire length of said drilling apparatus, and said last-named electrode being sufiiciently removed from said bore hole so that variations in electrical impedance of the strata adjacent the lower end of the drilling apparatus produce measurable variations in the measured electrical variable as said drilling apparatus is extended to different depths.

4. A method for determining variations in an electrical property of the strata at different depths traversed by a bore hole during the drilling of said bore hole, which comprises: passing an electric current through the earth between an electrode comprising a drilling apparatus extending within a bore hole, and another electrode connected to the earth at a position removed from said bore hole; taking a measurement of an electrical variable indicative of the electrical resistance of the path of said current through the earth; and repeating the passage of such current and the taking of such measurement as the drilling apparatus is extended to difierent depths within the bore hole, while maintaining said other Eelectrode substantially at a fixed position, said drilling apparatus being exposed to electrical contact with the wall of said bore hole throughout substantially its entire length whereby the flow of said electric current between the drilling apparatus and the earth is caused to take place throughout substantially the entire length of said drilling apparatus, and said last-named electrode being suificiently removed from said bore hole so that variations in electrical resistance of the strata adjacent the lower end of the drilling apparatus produce measurable variations in the measured electrical variable as said drilling apparatus is extended to different depths.

5. A method for determining variations in an electrical property of the strata at different depths traversed by a bore hole during the drilling of said bore hole, which comprises: passing an alternating electric current through the earth between an electrode comprising a drilling apparatus extending within a bore hole, and another electrode connected to the earth at a position removed from said bore hole; taking a measurement of an electrical variable indicative of the dielectric properties of the path of said current through the earth; and repeating the passage of such current and the taking of such measurement as the drilling apparatus is extended to different depths within the bore hole, while maintaining said other electrode substantially at a fixed position, said drilling apparatus being exposed to electrical contact with the wall of said bore hole throughout substantially its entire length whereby the flow of said electric current between the drilling apparatus and the earth is caused to take place throughout substantially the entire length of said drilling apparatus, and said last-named electrode being sufiiciently removed from said bore hole so that variations in dielectric properties of the strata adjacent the lower end of the drilling apparatus produce measurable variations in the measured electrical variable as said drilling apparatus is extended to different depths.

6. A method for determining variations in an electrical property of the strata at different depths traversed by a bore hole, during the drilling of said bore hole, which comprises: passing an electric current through the earth between an electrode comprising a drilling apparatus extending within a bore hole, and another electrode connected to the earth at a position removed from said bore hole; taking a measurement, in an electrical circuit associated with said electrodes, of an electrical variable indicative of the electrical conductivity of the path of said current through the earth; and repeating the passage of such current and the taking of such measurement as the drilling apparatus is extended to different depths within the bore hole, while maintaining said other electrode substantially at a fixed position, said drilling apparatus being exposed to electrical contact with the wall of said bore hole throughout substantially its entire length whereby the flow of said electric current between the drilling apparatus and the earth is caused to take place throughout substantially the entire length of said drilling apparatus, and said last-named electrode being sufficiently distant from said bore hole to cause a measurable portion of said current to flow through substantially the entire length of said drilling apparatus within the bore hole and to flow between the strata and the drilling apparatus adjacent the lower end of the drilling apparatus so that variations in the electrical conductivity of the strata adjacentthe lower end of the drilling apparatus. produce measurable variations in the measured electrical variable, as said drilling apparatus is extended to difierent depths.-

7. A method for determining variations in an electrical property of the strata at different depths traversed by a bore hole during the drilling of said bore hole, which comprises: passing an electric current. through the earth between an electrode comprising a drilling apparatus extending within abore hole, and another electrode connected to the earth at a position removed from said bore hole; taking a measurement, in an electrical circuit associated with said electrodes, of an electrical variable indicative of the electrical impedance of the path of said current through the earth; and repeating the passage of such current and the taking of such measurement as the drilling apparatus is extended to different depths within the bore hole, while maintaining said other electrode substantially at a fixed position, said drilling apparatus being exposed to electrical contact with the wall of said bore hole throughout substantially its entire length whereby the flow of said electric current between the drilling apparatus and the earth is caused to take place throughout substantially the entire length of said drilling apparatus, and said last-named electrode being sufliciently distant from said bore hole to cause a measurable portion of said current to flow through substantially the entire length of said drilling apparatus within the bore hole and to flow between the strata and the drilling apparatus adjacent the. lower end of the drilling apparatus so that variations in the electrical impedance of the strata adjacent the lower end of the drilling apparatus produce measurable variations in the measured electrical variable as said drilling apparatus is extended to different depths.

8. A method for determining variations in an electrical property of the strata at different depths traversed by a bore hole during the drilling of said bore hole, which comprises: passing an electric current through the earth between an electrode comprising a drilling,apparatus extending within a bore hole, and another electrode connected to the earth at a position removed from said bore hole; taking a measurement, in an electrical circuit associated with said electrodes, of an electrical variable indicative of the electrical resistance of the path of said current through the earth; and repeating the passage of such current and the taking of such measurement as the drilling apparatus is extended to different depths within the bore hole, while maintaining said other electrode substantially at a fixed position, said drilling apparatus being exposed to electrical contact with the wall of said bore hole throughout substantially its entire length whereby the flow of said electric current between the drilling apparatus and the earth is caused to take place throughout substantially the entire length of said drilling apparatus, and said last-named electrode being sufliciently distant from said bore hole to cause a measurable portion of said current to flow through substantially the entire length of said drilling apparatus within the bore hole and to flow between the strata and the drilling apparatus-adjacent the lower end of the drill ing apparatus so that variations in the electrical resistance of the strata adjacent the lower end of the drilling apparatus produce measurable variations in the measured electrical variable as said drilling apparatus is extended to different depths.

9. A method for determining variations in an electrical property of the strata at different depths traversed by a bore hole during the drilling of said bore hole, which comprises: passing an electric current through the earth between an electrode comprising a drilling apparatus extending within a bore hole, and another electrode connected to the earth at a position removed from said bore hole; taking a measurement, in an electrical circuit associated with said electrodes, of an electrical variable indicative of the dielectric properties of the path of said current through the earth; and repeating the passage of such current and the taking of such measurement as the drilling apparatus is extended to different depths within the bore hole, while maintaining said other electrode substantially at a fixed position, said drilling apparatus being exposed to electrical contact with the wall of said bo're hole throughout substantially its entire length whereby the flow of said electric current between the drilling apparatus and the earth is caused to take place throughout substantially the entire length of said drilling apparatus, and said last-named electrode being sufficiently distant from said bore hole to cause a measurable portion of said current tov flow through substantially the entire length of said drilling apparatus within the bore hole and to flow between the strata and the drilling apparatus adjacent the lower end of the drilling apparatus so that variations in the dielectric properties of the strata adjacent the lower end of the drilling apparatus produce measurable variations in the measured electrical variable as said drilling apparatus is extended to diiferent depths. I

10. An apparatus for use in determining the nature of the strata traversed by a bore hole, during the process of drilling said bore bola-which comprises: a drilling apparatus constituting an electrode and extending within a bore hole and exposed to electriqal contact with the wall of said bore hole throughout substantially its entire length; another electrode connected to the earth at a point removed from said bore hole; an electrical circuit associated with said two electrodes; and electrical measuring means associated with said electrical circuit, said last-named electrode being sufficiently distant from said bore hole so that measurements obtained on said measuring means are influenced to an important degree by an electrical property of the strata adjacent the lower end of said drilling apparatus.

11. An apparatus for use in determining the nature of the strata traversed by a bore hole during the process of drilling said bore hole, which comprises: a drilling apparatus constituting an electrode and extending within a bore hole and exposed to electrical contact with the wall of said bore hole substantially throughout its length; another electrode connected to the earth at a point removed from said bore hole; an electrical circuit associated with said two electrodes; means associated with said electrical circuit for passing an electric current through the earth between said electrodes; and electrical measuring means associated with said electrical circuit, said last-- named-electrode being sufflciently distant from said bore hole so that measurements obtained on said measuring means are influenced to an important degree by an electrical property of the strata adjacent the lower end of said drilling. apparatus.

12. An apparatus for use in determining the nature of the strata traversed by a bore hole during the process of drilling said bore hole, which comprises: a drilling apparatus constituting an electrode and extending within a bore hole and exposed to electrical contact with the wall of said bore hole substantially throughout its entire length; another electrode connected to the earth end thereof, so that the measurements obtained on said measuring means are influenced to an important degree by an electrical property of the strata adjacent the lower end of said drilling ap- I paratus.

13. An apparatus for use indetermining the nature of the strata traversed by a bore hole during the process of drilling said bore hole, which comprises: an electrical circuit including a drilling apparatus constituting an electrode and extending within the bore hole, another electrode connected to the earth at a position removed from said bore hole, and the portion of the earth included electrically between said electrodes; and electrical measuring means associated with said circuit, said electrical measuring means having sufficient time lag to minimize the effect of transitory variations in said electrical circuit and said last-named electrode being ,sufllciently distant from said bore hole so that variations obtained on said measuring means are in fluenced to an important degree by an electrical property of the strata adjacent the lower end of said drilling apparatus.

14. An apparatus for use in determining the nature of the strata traversed by a bore hole during the process of drilling said bore hole, which comprises: a drilling apparatus constituting an electrode and extending within a bore hole and exposed to electrical contact with the wall of said bore hole substantially throughout its length; another electrode connected to the earth at a point removed from said bore hole; an electrical circuit associated with said two electrodes; means associated with said electrical circuit for passingan electric current through the earth between said electrodes; and electrical measuring means associated with said electrical circuit and responsive to variations in the electrical conductivity of the earth included electrically between said electrodes, said last-named electrode being sufllciently distant from said borehole so that variations .obtained on said measuring means are influenced to an important degree by the electrical conductivity of the strata adjacent the lower end of said drilling apparatus.

15. An apparatus for use in determining the nature of the strata traversed by a bore hole during the process of drilling said bore hole, which comprises: a drilling apparatus constituting an electrode and extending within a bore hole and exposed to electrical contact with the wall of said g ance of the earth included electrically between said electrodes, said last-named electrode, beings sufiiciently distant from said bore hole so that variations obtained on said measuring means are influenced to an important degree by the electrical impedance of, the strata adjacent the-lower end of said drilling apparatus, I v

16. An apparatus for useindetermining the nature of the strata traversed by a bore hole during the process of drilling said bore hole, which comprises: a drilling apparatus constituting an electrode and extending within a bore hole and exposed to electrical contact with the wall of said bore hole substantially throughout its length; another electrode connected to the earth at a point removed from said bore hole; an electrical circuit associated with said two electrodes; means associated with said electrical circuit for passing a direct electric current through the earth between said electrodes; and electrical measuring means associated with said electrical circuit and responsive to variations in the electrical resistance of the earth included electrically between said electrodes, saidlast-name electrode being sumbiently distant from s'aid bore hole so that variations obtained on' said measuring means are influenced to an'important degree by the electrical resistance of the strata adjacent the lower end of said drilling amzparatus. v Y i 7 1'7. Inan apparatus for determining variations in an electrical property of the strataat different depths traversed byabore'hol'e during the process -of drilling said bore hole, the combination which comprises: a drilling apparatus constituting an electrode andfextending within a bore hole and exposed to electrical .contact with the wall of said bore hole substantiallygthroughout", its entire length! another electrode connected to the earth at aposition removed from said bore hole; and

' means for passing an electric current through the earth' between said electrodes, said last-named electrode being sufiiciently distant from said bore hole so that a measurable portion of said electric current will flow through substantially the entire length of said drilling apparatus within said bore hole and between the strata and said drilling apparatus adjacent the lower end thereof, whereby the flow of said current is influenced to an important degree by an electrical property of the strata adjacent the lower end of the drilling apparatus.

JOHN JAY JAKOSKY. 

